I have fixed bushy plans, enabled with the postgres -b option. Here is
proof from OPTIMIZER_DEBUG:
levels left: 7
(9 8 7 6 ): size=1 width=16
path list:
Nestloop size=1 cost=0.000000
MergeJoin size=1 cost=0.000000
clauses=(x5.y = x6.y)
sortouter=1 sortinner=1
SeqScan(6) size=0 cost=0.000000
SeqScan(7) size=0 cost=0.000000
MergeJoin size=1 cost=0.000000
clauses=(x7.y = x8.y)
sortouter=1 sortinner=1
SeqScan(8) size=0 cost=0.000000
SeqScan(9) size=0 cost=0.000000
The regression tests pass with bushy plans enabled. I am not sure if
the executor is actually using a bushy plan, though.
The old bushy code was poor. It tried to do bushy plans by modifying
the joininfo nodes. I removed all that code, and just do the join
search in make_rels_by_clause_joins(). This is much more logical, and
does not require the joininfo setup/cleanup that the old code attempted.
Frankly, I would like to enable bushy plans and right-handed plans by
default. The optimizer is now fast enough that a 9-table join is almost
instantaneous, even with bush plans. People are not sophisticated
enough to know when to enables these options themselves. I am not sure I
am either. I would like to enables both, fix whatever breaks, and
programmatically enable the options when they make sense.
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Bruce Momjian | http://www.op.net/~candle
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